Ask any group of professional
sports or wildlife photographers to name their favorite lens, and most
will mention a "fast" 500mm f/4 model with internal focusing and low dispersion
glass elements. Ideal in many respects, such lenses offer several advantages.
The long focal length allows for frame-filling images of distant subjects,
while the wide maximum aperture produces action-stopping shutter speeds.
The premium-grade optics generally provide razor-sharp images, while internal
focusing offers high autofocus speed.

Many serious photo enthusiasts
would love to own a 500mm f/4 lens, but few can justify such a large,
heavy, expensive model for personal use. If you fall into this category,
Sigma may have the solution: the autofocus APO 500mm f/4.5 EX HSM that
I tested while photographing wading birds in Southwest Florida. It's currently
the only "fast" independent brand 500mm lens and the only model of this
type that's available in mounts for certain brands of cameras. Granted,
the f/4.5 maximum aperture is smaller than f/4, but that allowed Sigma
to make this lens substantially smaller and lighter. At a street price
of under $3500--including a rotating Circular polarizer--it may not be
"inexpensive," but it does fall within the reach of more photo enthusiasts
than the f/4 alternatives.

Technical Overview
This Sigma lens exhibits a professional look and feel, with its rugged
metal barrel, matte black finish, 2.5" wide rubberized focusing ring,
large controls, deep lens hood, and rotating tripod mounting collar. To
minimize the search for focus, a three-stage focus limiter switch is provided.
Manual focus operation is well damped with adequate friction for a familiar
"feel." A front element of clear, optical glass protects the more expensive
elements; it can be replaced by Sigma if scratched. Sigma indicates that
all of the optical elements are made of "lead and arsenic free ecological
glass."

Although this lens does not
include a system that would compensate for camera shake, the designers
did incorporate all of the other essentials. These include two Extra Low
Dispersion (ELD) elements, internal focusing, rear filter holder, and
compatibility with tele-converters. Models in Canon EF, Nikon (D), and
Sigma SA mount also include Sigma's Hyper Sonic Motor (HSM). This provides
fast, nearly silent operation and reliable tracking focus. With the HSM
models, you can also override autofocus at any time, without switching
over to manual focus.

Models in other mounts employ
the camera's focus motor, for conventional AF operation. Regardless of
the mount, all include Internal Focusing. This can help to maximize AF
speed because less mass must be moved. The physical length of the lens
also remains constant so the center of gravity does not shift, important
when working with a tripod or monopod.

The designers specified ELD
elements to compensate chromatic aberration, essential with a wide aperture
telephoto lens of high quality. Without getting into a lengthy discussion
about aberrations, let's just consider the benefits of such elements.
They help to produce higher sharpness and superior color reproduction
without color fringing around edges of a subject. These benefits are most
obvious at wide apertures, where long lenses are generally used. In fact,
as we'll see, this Sigma super-tele is optimized to produce the best results
without stopping down to mid-sized apertures.

General Performance
During a late winter trip to Florida, I photographed egrets, herons, and
white pelicans on Sanibel Island, at the rookery in Venice, and at several
other locations. This Sigma lens was fully compatible with all of the
high-tech capabilities of a Canon EOS-3, even when I used the Sigma EX
APO 1.4x tele-converter. Although the effective maximum aperture was smaller
than f/5.6 with that accessory, this camera--like the EOS-1 V--maintained
autofocus, using only the single, central AF sensor.

Note: With this f/4.5
lens, other cameras disengage AF when any tele-converter is used, the
primary drawback of a lens with a maximum aperture smaller than f/4. This
is a compromise, but was necessary in order to keep the Sigma AF APO 500mm
f/4.5 EX HSM model compact, lightweight, and reasonably priced. Do note
that all cameras disengage AF when a 2x tele-converter is used even on
a lens with a maximum aperture of f/4.

Because the effective maximum aperture reduces to f/6.3
when a 1.4x tele-converter is used with this f/4.5 lens,
most cameras disengage autofocus. However, AF operation
is maintained with a Canon EOS-3 or an EOS-1 V, using the
central focus detection point. (At 720mm at f/6.3; Fujichrome
Sensia 100.)

Autofocus performance was exceptional
when I used the lens alone: incredibly fast and silent thanks to the HSM
focusing system. With the EOS-3, focus acquisition in moderately low light
(before sunrise at the rookery) was also impressive. I really appreciated
the ability to quickly fine-tune focus manually at any time: on a pelican's
eye instead of its beak, for example. When I added the 1.4x tele-converter,
autofocus remained reliable with slow-moving birds building a nest, but
was not as effective in Continuous AF. This is understandable, considering
the loss of light to the AF sensor.

Optical Performance
Since a lens of this type is most frequently used at wide apertures, I
made most of my images at f/4.5 and at f/5.6. To minimize blur from camera
shake, I used a rigid Bogen/Manfrotto 3000-series tripod, an Arca Swiss
B-1 head with quick-release clamp, and a long Kirk Enterprises mounting
plate. After discarding slides that were unacceptable due to camera or
subject movement, I checked the others under a high quality 8x loupe.

The results of my field tests
are impressive indeed. The slides made at 500mm are extremely sharp with
very high resolution; even the finest detail in feathers is crisply defined.
I found no evidence of color fringing whatsoever, as this Sigma lens delivered
first-class results. Flare control was very effective, in spite of the
many lens elements and numerous air-to-glass surfaces, thanks to internal
precautions and the deep lens hood. Except in images made while shooting
toward the morning sun at the "Ding" Darling NWR, veiling glare (a sign
of flare) is not visible in any of my slides.

I occasionally stopped down to f/8 or f/11 for increased
depth of field, but this tactic is not necessary to maximize
image quality. The Sigma 500mm f/4.5 lens produces similar
sharpness and resolution at all f/stops from f/5.6 to f/11.
(At f/8; tripod; Fujichrome Provia 100F.)

At f/4.5 the lens produced
very high sharpness, rating an 8 on my subjective scale of 1 to 10. The
results were similar at f/5.6, with slightly higher edge sharpness, for
an overall rating of 8.5, adequately high for an excellent 11x14" print
or a full-page spread in a magazine. Image quality was very similar from
f/5.6 to f/11. There was absolutely no need to stop down to smaller apertures,
confirming that the lens is optimized for shooting at wide apertures.
This consistency of fine performance is also a sign of a well-designed
optical formula. With the EX APO 1.4x tele-converter, image quality was
still very good at the widest aperture (an effective f/6.3) rating a 6.5.
Edge sharpness increased at f/8, leading to a rating of 7, adequate for
an excellent 8x12" print. Since a 2x tele-converter would have reduced
the effective maximum aperture to f/9--seriously increasing the risk of
blur from any vibration--I did not test the Sigma telephoto with that
accessory.

Final Assessment
Even with the most expensive professional telephoto lens, technical proficiency
is a prerequisite for sharp images at high magnification. For optimum
results, use a rigid tripod and head at all times. If your camera has
a reflex mirror pre-lock control, use it to raise the mirror in advance
with static subjects. This precaution is most important at shutter speeds
in the 1/4-1/60 sec range where internal vibration from mirror action
is most likely to degrade sharpness. Because there's very little depth
of field to mask any focus error, focus carefully and precisely on the
most essential subject element.

During the test period, the
Sigma AF APO 500mm f/4.5 EX HSM met my needs for professional stock photography.
My best images will certainly satisfy critical agency editors and photo
buyers. While I cannot confirm its reliability during extensive use over
months or years, friends who own this lens speak highly of its ruggedness,
as discussed in our sidebar. Another Sigma lens--the AF APO 70-200mm f/2.8
EX HSM zoom--has provided me with two years of trouble-free service. This
500mm super-telephoto model should be just as dependable. Considering
its fine performance, and moderate size, weight, and price, this lens
would make a fine addition to any serious outdoor photographer's arsenal.

Len and Chris Maltese work with their Sigma AF APO 500mm
f/4.5 EX HSM lenses in this image made during our visit
to the rookery in Venice, Florida. Both are fully satisfied
with the lens, citing the fine mechanical and optical qualities
of this relatively affordable model.

Sigma AF APO 500mm f/4.5
EX HSM: Long-Term Evaluation
Although I shot over 20 rolls of film with this Sigma super-tele lens,
I decided to ask two friends for comments about their long-term experiences
with the same model. Chris and Len Maltese are avid bird photographers
who both own this 500mm f/4.5 lens. Chris acquired one some two years
ago, while Len followed suit a year later. As Len recalls, he bought the
lens based on his brother's recommendation, favorable reviews, and past
experience with the brand. "I have owned other pro Sigma lenses in the
past, and was very happy with the performance and quality."

Both photographers remain completely
satisfied with their purchase, speaking highly of its optical capabilities
and mechanical reliability. They agree that image quality is "excellent."
With the EX APO 1.4x tele-converter, they rate it as "very good" to "extremely
good." When used with the 2x EX APO accessory, sharpness remains "good,
though the slides are not as crisp," according to Len. Chris uses the
lens on Nikon bodies, usually an F5, while Len's preferred camera is an
EOS-1 V. "It functions flawlessly in all modes and autofocus is fast and
quiet," they both confirm. "Metal construction makes this a very rugged
piece of equipment," according to Len. "Even so, it's not overly heavy
so you can carry it over a shoulder for hours, attached to a tripod, and
still feel fine at the end of the day."

"For the price, this lens is
outstanding," Chris concludes. "If you're looking for a super-telephoto
lens--and don't want to add a second mortgage to your house to pay for
it--the AF APO Sigma 500mm f/4.5 EX lens is the way to go," Len adds.
To view some of the photographers' images, visit their web site www.maltese.net.